This invention relates to a driving shaft including at both the ends yokes constituting parts of respective universal joints and an intermediate slidable portion composed of a male shaft member and a female shaft member fitted with each other by means of splines, and more particularly to a method for producing the driving shaft.
With a driving shaft of this kind, it is often desirable that either the male shaft member or the female shaft member is axially contractible when being subjected to axial stresses causing the driving shaft to be contracted in excess of its predetermined elongation and contraction strokes. For this purpose, it has been proposed that a male or female shaft member is composed of at least two parts which are connected to each other by means of shear pins which may be broken when a predetermined load is applied thereto. It has also been proposed that either a male shaft member or a female shaft member of a driving shaft is connected to an axially contractible tube in order to make it possible for the driving shaft to contract axially when stresses in excess of a predetermined value are axially applied thereto. Moreover, it has been proposed to connect the two parts aforementioned by means of a snap ring, key, spline fitting in metal to metal contact, or adhesive.
With the shear pins described above, the connecting portions for the two parts are located only at two diametrically opposed positions, so that when the pins are progressively fatigued in use for a prolonged period of time, the load to be controlled by the pins would be changed. In other words, the limit of load determined by the pins would become lower than the initially aimed limit of load. With the use of deformable tube, moreover, it would be difficult to control the load at which the tube exhibits its effective performance. Namely, it would be difficult to determine the limit of load at which the tube starts to contract.